This invention relates to an instrument encapsulated within a shell and, more particularly, to a header assembly including a hybrid amplifier, the header assembly capping the instrument shell and having a low profile so as to reduce the overall length of the instrument.
U.S. Pat. No. 4,621,529 discloses an angular rate sensor assembly instrument which includes a gyroscopic element having a spin axis and a flexure hinge for resiliently mounting the gyroscopic element to a base. The sensor assembly further includes a torque sensing assembly which has a piezoelectric beam mounted in coaxial relation to the spin axis. A first beam restraining member mounts a first edge portion of the piezoelectric beam to the gyroscopic element and a second beam restraining member mounts an opposite edge portion of the piezoelectric beam to the base. The piezoelectric beam is adapted to generate an electrical signal proportional to the angular velocity of the sensor assembly about an axis perpendicular to the spin axis. The entire instrument is contained within an instrument shell which also holds a motor for driving the gyroscopic element and electronic circuitry, including a buffer amplifier, to provide an output signal derived from the piezoelectric beam electrical signal, which output signal is suitable for driving electronics to which the instrument is connected.
In recent years, there has been interest in reducing the overall length of such an encapsulated instrument. One limiting factor in the past has been the packaging of the buffer amplifier. Such an amplifier is typically of "hybrid" design, which is a mixture of discrete and printed circuitry within a hermetic enclosure. In the past, the hybrid amplifier was built up into a standard rectangular "flat-pack" case, with its own glassed in headers. This amplifier package, in turn, was bonded to the inside surface of a glass to metal seal header plate, the header plate forming an outside end of the hermetically sealed instrument. Electrical wires are soldered between the instrument's active components, the terminals of the flat-pack amplifier, and from these terminals to the inside of the instrument's glassed in terminal pins. Spacers are provided for the routing of wires around and between the flat-pack case and the header plate. This results in a redundant set of hermetic glass to metal sealed terminals, a redundant enclosure, and numerous flying wire leads that run between the amplifier and the header plate. With this arrangement, the sealed and tested amplifier is provided to the instrument assembly operation for installation to the header plate and subsequent wiring. The assembly of amplifiers, wiring and header plate is not tested again until top level instrument testing is performed.
It is therefore a primary object of the present invention to provide an arrangement which reduces the overall length of such an instrument.
It is a further object of the present invention to provide an arrangement which simplifies the internal wiring connections to the header plate.
It is another object of the present invention to provide a header assembly including a hybrid amplifier which can be tested as a complete module.